.003" (that's .07362mm for those of you in Stuttgart) has been removed from the sealing surface to true it up.

When I was cataloging the hardware I noticed that a couple studs from the exhaust had aluminum in the threads. A quick call to Anchor Atlantic and he installed helicoils in the affected holes, and replaced the studs with new ones.

Note that my name has been stamped into the non-mating area of the head. Which doesn't bother me; this car is going to pass by Will, not by sale!

The precision of a burette makes careful measurement with a burette very important to avoid systematic error. When reading a burette, the viewer's eyes must be at the level of the graduation to avoid parallax error. Even the thickness of the lines printed on the burette matters; the bottom of the meniscus of the liquid should be touching the top of the line you wish to measure from. A common rule of thumb is to add 0.02 mL if the bottom of the meniscus is touching the bottom of the line. Due to the precision of the burette, even a single drop of liquid hanging from the bottom of a burette should be transferred to the receiving flask, usually by touching the drop to the side of the receiving flask and washing into the solution with the experimental solvent (usually water). Through careful control of the stopcock and rinsing, even partial drops of liquid can be added to the receiving flask.

2. Because it's a 50cc burette, it obviously has to be refilled once after you dump 50cc into the head. Take care that when filling the burette (I used a funnel) that you don't dump washer solvent down the sides, it will drip down into the head.

3. Parallax error is pretty significant. The surface of the fluid in the burette forms a curve or "meniscus" due to air pressure and surface tension. The BOTTOM of the meniscus should be touching the TOP of the line, and you should not be able to see the line on the other side of the burette. If you can see it, you've got parallax error. This requires a lot of standing and sitting.

4. Don't let the tip of the burette get more than about 1/4" from the surface of the liquid, or you will get air bubbles in the liquid that will screw up the measurement.

5. I used an old CD as a cover for the chamber. While functional, a nice piece of plexiglas cut to exactly 88.4mm diameter would be better, as you can use a smaller hole. Be sure to put plenty of grease around the edges of the CD to seal it, otherwise the solvent will leak out. I used Bosch distributor grease because that's what I happened to have around, but any old grease would do.

6. Repeat repeat repeat the measurements. You will probably not get consistent measurements the first time out. A source of error for me was the fluid in the spark plug. I used NGK BP7ES plugs, because that's what I'll use on the road, and these hold about 1.5cc of solvent around the insulator. If you don't flush all of that out after the first measurement, then you will get a measurement that's less than your first one, because the plug is already full.

7. Be sure to shoot the head inside and out with WD-40 to eliminate any moisture after the process. The washer solvent is water and alcohol based so you don't want it lingering and causing rust between now and engine assembly.

Well, at first blush these measurements will require some adjustments to get all the compressions equal.

With a 36cc dome volume, varying deck heights are required to get the compressions down to a reasonable range. Even then, using thicker spacers in multiples of .25mm (not stacked) (the base 1.0mm deck height presumes a .25mm spacer) still results in varying compressions. The calculation is sensitive to dome volume: decreasing dome volume reduces the variation, but the overall effect is to decrease compression, of course.

Which troubles me, because the target deck height I want to use is 1.0mm and no greater. For example, in order to accomodate the much lower head volume for cylinder Nr. 3, a deck height of 1.5mm must be used.

So, my next step is to CC the heads again, this time with more precision, to be absolutely certain of the measurements. Once that's done, I can then consider whether increasing the combustion chamber volume on all the heads to 71.5cc makes sense. Obviously it's advantageous to use a smaller dome volume on the piston and stick with the smaller chamber volume to make the desired compression, but if that comes at the result of increasing the deck height it's a less than optimum tradeoff.

Of course, this is with a theoretical deck height of 1.0mm. In practice, the actual deck height will vary.

What would you pros do? Get a different head for Nr. 3? Or have the valve seats ground again to sink the valve deeper? Relieve the head near the spark plug hole with a die grinder? Ignore it?

Well, I ordered a couple sheets of 3/8" plexiglass and a circle cutter. I'm going to fab up a plate that's exactly 88.4mm diameter and put a very small hole in it, level the head with a wedge and get the exact measurement. I'm also going to blow any remaining fluid out of the spark plug hole with compressed air to make sure it doesn't throw off the measurements.

If a second set of repeatable measurements confirms, then I'm going to relieve the head around the spark plug recess. This should unshroud the plug a bit while removing the requisite amount of metal to even out the compression ratios.

Are these heads brand new? The reason I ask is it does not look they they have been machined for flatness...I noticed that on most of the heads that I have taken off they require a teeny bit of machining to make them flat again.....its hard to tell from the photos...

I think you are on the right track with thicker Plexiglass and a smaller hole. A CD is too thin and flexible. That plus the meniscus effect on the large hole in the center of the CD will introduce too much variation in the measurement.

I used the thick Plexiglass with a small hole that was only slightly larger in diameter than the burette discharge. I was able to repeat the head volume on my RSR spec heads to within +/- 0.5 cc.

The biggest challenge was chasing all of the air out of the head and eliminating the air bubble without leaking fluid out the outer edges of the Plexiglass disc.

Well, trying to fab plexiglass circles with a fly cutter nearly resulted in the severing of one of my fingers. I don't recommend it.

What I did instead was order some plexiglass discs made with a freaking CNC router, to a tolerance of 0.1mm! And they were still slightly too big, so I had to trim the edge with a dremel. But once I finished, they were a nice press fit in the recess in the head.

I then used Bosch distributor grease to seal the edge. You don't run a big bead of grease, just put the tip of the tube against the edge of the disc and squeeze the tube slightly as you rotate the disc. This puts a very thin film on the disc that seals nicely once you turn it a bit.

Also, following Tom's advice, I used a very small hole in the disc. With this done, I found it VERY easy to get repeatable measurements, within three tenths of a cc. And guess what? The errors I saw using the CD disappeared!

All the heads were within three tenths of 72 cc's exactly. I have to give the Germans credit for having the precision, 40 years ago, to make the combustion chambers exactly the same size. It helps that there was only one valve job in the past and that I used NOS and new valves in the heads, making it easy to set them all at the same height.

So now I have the information I need for exact CR calculations. The moral: do it RIGHT with the right stuff the first time!

I also have a few extra plexiglass discs, you won't believe how expensive they were, but if anybody wants one, I'll let you have one for my cost, which is pretty darned expensive. They only work with 2,0 heads.

I'm not so sure about your logic here... you are using different size shims to change the deck height based on measurements of dome volume and assuming everything else is the same... You could be screwing yourself IMHO. What if the difference in dome volume were, as you kinda mentioned, in the spark plug hole, or a slightly different casting that day. If you set your shim size this way I think you might end up skewing the carrier or something like that. You may wish to determine the cyl top to crank center distance as well as the bottom head sealing surface to top of head sealing surface to see if your cam carrier will be torqued flat... hehehe assuming it remains flat while torqued...

It seems to me that you will have to live with the individual differences in compression/deck height if you want it all to be flat on the top...

I'm not so sure about your logic here... you are using different size shims to change the deck height based on measurements of dome volume and assuming everything else is the same... You could be screwing yourself IMHO. What if the difference in dome volume were, as you kinda mentioned, in the spark plug hole, or a slightly different casting that day. If you set your shim size this way I think you might end up skewing the carrier or something like that. You may wish to determine the cyl top to crank center distance as well as the bottom head sealing surface to top of head sealing surface to see if your cam carrier will be torqued flat... hehehe assuming it remains flat while torqued...

It seems to me that you will have to live with the individual differences in compression/deck height if you want it all to be flat on the top...

+1
Work from the centerline of crank out.
Blueprint the case, making sure the cylinder spigot bores are in spec then work out from there reducing tolerance buildup all the way out to the cam towers.

Well, the good news is that I will be using the standard .25mm shims all the way around. Spigot height is the same all around and the heads are all the same height so it should be smooth sailing.

I agree, Michael: in retrospect it would have been a bad idea to have widely varying shims because the cam tower would have a hard time fitting squarely. The thing to do if different-size chambers are encountered is to relieve the head around the spark plug recess, or weld it up, but the latter very exotic.

Fortunately this is not a challenge I will be facing because all the heads are the same within a couple tenths.

I do basically the same only do the final? CR and deck with the engine partially assembled. This allows you to choose the heads matched closer for each side. My final measurements are with the sparkplug vertical. I have a plug with some drill rod welded to it to make measuring vertical easier. I then use a sparkplug with the ceramic taken out and a piece of steel tubing installed. I know the volume of the hollow plug.

For testing I even grease the valve-to-seat contact and the top ring

There used to be cylinder base gaskets in 0.05 mm steps. The important aspects are to use three identical (if the case is straight) on each side.

After you are satisfied with the CR, check the clearances again.

Did you install the longer intake studs so you can use the phenolic insulating spacers (I use two at each port)? These spacers were sized for T ports.